This invention relates to a focused ion beam apparatus and a method for using the apparatus. The apparatus and method are used for processing a predetermined area on a sample by irradiation with the focused ion beam and by scanning, and/or observing the sample surface by detecting secondary particles generated by the irradiation with the focused ion beams.
A focused ion beam apparatus of the prior art will be described below with reference to FIG. 5. As shown in Tokkaisho 59-16852, the focused ion beam apparatus in the prior art includes a sample chamber 1, an ion beam irradiation unit 2 having an extraction electrode for extracting ions from a liquid metal ion source of Ga, etc., an aperture and an electrostatic electrode for focusing the ions into a focused ion beam 11, and a deflection electrode for directing the focused ion beam 11 at the predetermined area of the sample 5 surface by deflecting and scanning the focused ion beam 11. By repeated irradiation at the sample 5 surface with the focused ion beam 11, the sample 5 surface at the predetermined area is sputtered with the focused ion beam 11. In this manner, the etching process for forming a vertical side wall on the sample 5 is performed. That is, the surface portion of the sample 5 is processed to form a section. And the secondary particles generated by the irradiation at the section with the focused ion beam are detected by a detector 6, and then the image of the section is displayed on the display 7.
Ions, which are used for the focused ion beam processing on the sample in the prior art, are doped into the sample. By the phenomenon of the doped ion, the characteristics at the area irradiated with the focused ion beam are changed. Next, an example using Ga as the ion source of the ion irradiation unit which irradiates, with the focused ion beam, a Si substrate 36 as the sample 5 will be explained below with reference to FIG. 6A. A Ga ion beam 11 having high energy impacts the Si substrate 36. As a part of the Ga ions 37 are doped at the Si substrate 36, the processed and displayed area of the sample 5 is contaminated. As especially, Ga is one of the Group III elements, Ga in the Si substrate 36 behaves as a P-type impurity and forms impurity diffusion area 35. And then the distribution of the impurity diffusion concentration of sample 5 changes. Ga ions 37 dope at a high diffusion rate, react with Al which is used as a wiring and then the Al wiring is highly eroded by Ga ions. When such a contaminated sample 5 or a Si substrate 36 is returned to a manufacturing process, the Ga which has been doped in the substrate 36, auto-dopes itself in heating processes and manufacturing apparatuses used in such processes can be contaminated with Ga. Therefore, the sample 5 which is processed and/or observed with the focused ion beam apparatus can not be returned into the manufacturing process, which is a problem.